For a number of known reasons, bone fixation devices are useful for promoting proper healing of injured or damaged vertebral bone segments caused by trauma, tumor growth, or degenerative disc disease. The external fixation devices immobilize the injured bone segments to ensure the proper growth of new osseous tissue between the damaged segments. These types of external bone fixation devices often include internal bracing and instrumentation to stabilize the spinal column to facilitate the efficient healing of the damaged area without deformity or instability, while minimizing any immobilization and post-operative care of the patient.
One such device is an osteosynthesis plate, more commonly referred to as a bone fixation plate, that can be used to immobilize adjacent skeletal parts such as bones. Typically, the fixation plate is a rigid metal or polymeric plate positioned to span bones or bone segments that require immobilization with respect to one another. The plate is fastened to the respective bones, usually with bone screws, so that the plate remains in contact with the bones and fixes them in a desired position. Bone plates can be useful in providing the mechanical support necessary to keep vertebral bodies in proper position and bridge a weakened or diseased area such as when a disc, vertebral body or fragment has been removed.
Such plates have been used to immobilize a variety of bones, including vertebral bodies of the spine. These bone plate systems usually include a rigid bone plate having a plurality of screw openings. The openings are either holes or slots to allow for freedom of screw movement. The bone plate is placed against the damaged vertebral bodies and bone screws are used to secure the bone plate to the spine, usually with the bone screws being driven into the vertebral bodies. Exemplary systems like the one just described can be found in U.S. Pat. No. 6,159,213 to Rogozinski, U.S. Pat. No. 6,017,345 to Richelsoph, U.S. Pat. No. 5,676,666 to Oxiand et al., U.S. Pat. No. 5,616,144 to Yapp et al., U.S. Pat. No. 5,549,612 to Yapp et al., U.S. Pat. No. 5,261,910 to Warden et al., and U.S. Pat. No. 4,696,290 to Steffee.
Despite the existence of these bone plate systems, there remains a need for an anterior bone plate system that minimizes any soft tissue and osseous tissue damage that would occur with its implementation and still be easy to use. The system must be able to provide effective fixation and immobilization of vertebral bodies, while also providing for the subsidence necessary for proper fusion and prevent axial extension of the plate.